animals Article Social Behaviour of Horses in Response to Vocalisations of Predators Iwona Janczarek 1 , Anna Wi´sniewska 1 , Michael H. Chruszczewski 2, Ewelina Tkaczyk 1 and Aleksandra Górecka-Bruzda 3,* 1 Department of Horse Breeding and Use, Faculty of Animal Sciences and Bioeconomy, University of Life Sciences in Lublin, 20-950 Lublin, Poland; [email protected] (I.J.); [email protected] (A.W.); [email protected] (E.T.) 2 Faculty of Psychology, University of Warsaw, 00-183 Warsaw, Poland; [email protected] 3 Department of Animal Behaviour and Welfare, Institute of Genetics and Animal Biotechnology, Polish Academy of Sciences, Jastrz˛ebiec,05-552 Magdalenka, Poland * Correspondence: [email protected]; Tel.: +48-22-736-71-24 Received: 12 November 2020; Accepted: 4 December 2020; Published: 8 December 2020 Simple Summary: Animal social strategies are of importance when avoiding predation. Since horses are the least hunted among all farm animal species, we suppose that the alert reaction to a predator’s vocalisation, followed by anti-predator social behaviour, still exists in domestic horses. Recorded vocalisations of three different predators (grey wolf, Arabian leopard and golden jackal) were played to 20 horses of two horse breeds—namely, Konik polski and Arabian. Social responses and tactics in antipredator behaviour differed between the breeds and between predators. Koniks exposed to vocalisations of a howling wolf resulted in tight groupings, while Arabians exposed to the growling of a leopard responded with linear group formation. The behaviour of studied horses, expressed by alertness and defensive formations, indicates existence of the social anti-predator behavior, which in turn may explain the low rates of horses falling prey to predators as compared with other farm animal species. Abstract: We tested the hypothesis that social defensive responses to the vocalisation of a predator still exist in horses. The recordings of a grey wolf, an Arabian leopard and a golden jackal were played to 20 Konik polski and Arabian mares. Durations of grazing, standing still, standing alert and the number of steps in walk and trot/canter were measured. In one-minute scans, the distances of the focal horse from the reference horse (DIST-RH) and from the nearest loudspeaker (DIST-LS) were approximated. The vocalisation of a leopard aroused the Arabians more than the Koniks (less grazing, stand-still and walk, more stand-alert and trotting/cantering). Koniks showed more relaxed behaviours to the leopard vocalisation (more grazing, stand-still and walk), but high alertness to the wolf playback (stand-alert, trotting/cantering). Spatial formation of the herd of Koniks showed tight grouping (lower DIST-RH) and maintaining distance from the potential threat (DIST-LS) in response to the wolf howling, while the Arabians approached the loudspeakers in linear herd formation when the leopard growls were played. Adult horses responded to potential predation by changing spatial group formations. This ability to apply a social strategy may be one of the explanations for the least number of horses among all hunted farm animal species. Keywords: horse; predator; vocalisation; social defensive behaviour; grey wolf; Arabian leopard; golden jackal Animals 2020, 10, 2331; doi:10.3390/ani10122331 www.mdpi.com/journal/animals Animals 2020, 10, 2331 2 of 18 1. Introduction Farm animals have been predated by large carnivores from the beginning of domestication, e.g., [1–4]. The damages to livestock caused by predation [5,6], as well as the cultural and public fear of predators [7–9] has resulted in the almost total extermination of the majority of large predators [10]. This applies to the grey wolf (Canis lupus) in North America and Europe, jaguars (Panthera onca) in Central and South America, Arabian leopards (P. pardus nimr), African wild dogs (Lycaon pictus) in Africa and tigers (P. tigris) in Asia [7,11]. In Europe, four big carnivore species, the brown bear (Ursus arctor), the grey wolf (Canis lupus), the Eurasian lynx (Lynx lynx) and the wolverine (Gulo gulo), were almost driven to extinction in the last century. However, the populations of certain predator species, such as golden jackal (Canis aureus) in Africa and Asia [12], remain at a stable level. It has been observed that due to recent snowless winters, this species has been able to colonise new habitats in Europe [13,14]. The protection programmes introduced in America and Europe enabled saving of the last wild wolves, bears and lynxes by providing compensations to farmers for killed livestock [9,15]. With a confirmed increase in the population of wolves, the problem with depredation has recently recurred [16]. According to [17], to an extent wild prey animals are able to counteract predation. For example, bold bighorn ewes (Ovis Canadensis) demonstrated low rates of being preyed upon [18], while male roe deer (Capreolus capreolus), who are more active than females, more successfully avoided predation from red foxes (Vulpes vulpes) [19]. Considering the high levels of vulnerability of domestic animals to depredation, it has been suggested that the decrease in the ability to counteract the depredation is likely due to the selection for tameness in cattle [20,21], sheep [22,23] and horses [24,25]. Leopards were observed to prey also on small domestic animals [4,26]. Although it was proposed that the predispositions (including tameness) to being domesticated are embedded in their nature [27], it is clear that, before domestication, these animals were able to avoid predation sufficiently to assure the survival of the species in natural habitats. Among all farm animals, horses are the least predated upon species [9]. It is not known if this is related to the overall smaller number of horses compared with other farm species or to their specific behaviour in response to predators. Horses are a highly vigilant species and easily express alert and/or flight behaviour, as confirmed by all studies on equine temperament and personality [28]. The tendency to react with fear is deeply rooted in the equine personality and very difficult, if even possible, to eradicate. The fearfulness, proposed as one of the personality traits in horses [24,29,30] and other animals [31] has been explained as basic, genetically imprinted response enabling threat avoidance [29]. Although this characteristic can cause troubles for humans, it has functional significance to horses as it allows them to avoid predation. The purported predator-related response has been used to exemplify equine avoidance of humans in so-called “natural” training methods [32]. Although the simple translation of horse anti-predatory behaviour into an avoidance response to humans was criticised [33], it is striking that only four reports on horse reactions to predator cues could be found in the scientific literature [24,25,34,35]. The fear response of prey animals to predators involves the processing of complex cues involving visual, olfactory and auditory stimuli. The studies on the behavioural and physiological (activation of the hypothalamic–pituitary–adrenal axis) responses to separate olfactory and auditory predator cues showed that they still evoke the instinctive state of fear in domestic horses [24,25]. In the cited studies, only the responses of individually tested horses were examined. However, most of the farm animal species are social; thus, instinctive social behaviour against predators may be of importance when avoiding predation [20,36]. It was recently confirmed by our studies [34,35] that the heart rate of horses increases during exposure to predators vocalisation. To our knowledge, the response of equine social groups (herds) to the presence of predator cues was not previously examined scientifically except for the latter studies. In this study, we tested the hypothesis that the social behavioural response of horses to a type of predator cue, namely the auditory stimulus, still exists in domestic horses. We chose only vocal cues, Animals 2020, 10, 2331 3 of 18 as it was observed that predators vocalise before [37] or during the chase or harassment of prey [38]. As the method of hunting differs between canids and large cats (chasing or stalking, [20], we also investigated the effect of predator species on the behaviour of horses. 2. Material and Methods 2.1. Ethical Note The procedures were conducted with permission (27/2016 issued on 13 May 2016) of the Local Commission for Ethics in Animal Experimentation, Lublin, Poland. 2.2. Animals The behaviour of horses monitored with heart rate recorder in [34] was observed. Twenty adult horses (all mares), 10 Konik polski horses (Koniks) and 10 Arabian pure breed horses (Arabians), from two different farms, located at a distance of 60 km apart (Koniks: 51◦320 N, 22◦970 E and Arabians: 50◦960 N, 23◦070 E) were tested. The horses were 5–15 years old, were clinically healthy and had not been used for riding for at least 3 years. In both farms, located far from busy roads, the horses were submitted to necessary husbandry procedures (hoof trimming, herding, deworming, etc.) and were exposed to the sounds of routine agricultural works. They were kept in 3 3 m boxes with straw × bedding and were out on grassy paddocks always in the same, socially stable group for at least 5 h daily. The horses were fed hay and oats twice daily with water and mineral salt blocks available ad libitum. They were habituated to humans during daily handling. For this study, before each test, the horses were identified with non-permanent numbers marked on their hindquarters. 2.3. Experiments Two large predators: the wolf (Canis lupus) and the Arabian leopard (Panthera pardus nimr) were chosen for the experiment. The vocalisation of the golden jackal (Canis aureus), a smaller opportunistic feeder, was chosen as the control sound. The recordings of the wolf howls (W), Arabian leopard roars (P) and jackal barking howls (J) were obtained from the archives of the Department of Zoology and Animal Ecology, the University of Life Science in Lublin.